1. Field of the Invention
The present invention generally relates to an apparatus for inputting coordinates, and more particularly to an apparatus for inputting desirable coordinates representative of a position of a cursor on a screen of a display unit provided in a personal computer system, for example.
2. Prior Art
Conventionally, a mouse device is well known as the apparatus for inputting coordinates (such as a pointing device) for use in a personal computer system. Such mouse device can be classified as a mechanical mouse device or an optical mouse device.
FIG. 1 is a diagrammatic view showing a mechanical constitution of the conventional mechanical mouse device surrounded by an X-axis and a Y-axis. In FIG. 1, 1 designates an X roller and 2 designates a Y roller. These rollers 1 and 2 are arranged by forming a right angle between axis directions of the rollers 1 and 2. In addition, 3 designates a dummy roller and 4 designates a metal ball. The metal ball 4 is supported by the rollers 1 to 3 so that the metal ball 4 can revolve freely. Furthermore, 5 and 6 designate increment type rotary encoders. The rotary encoder 5 outputs a pulse signal in response to a revolving distance of the X roller 1, and the rotary encoder 6 outputs a pulse signal in response to a revolving distance of the Y roller 2. Each of these rotary encoders 5 and 6 comprises a disc having a circumference on which a plurality of slits are formed by an equal distance, and a photo-interrupter for detecting the slits. These disc and photo-interrupter (not shown) are stored in a case. This case has a window at a predetermined position on a lower surface thereof, and a certain portion of the metal ball 4 is slightly stuck out of the window of the case.
The above-mentioned mouse device is used by being put on an upper surface of a desk, for example. When an operator of the personal computer system holds and slides such mouse device on the desk, the metal ball 4 must be revolved in accordance with a movement of the mouse device. Due to a revolution of the metal ball 4, the X roller 1 and the Y roller 2 must be revolved. In this case, the rotary encoder 5 outputs a pulse signal corresponding to a moving distance of the mouse device in the X direction. Similarly, the rotary encoder 6 outputs a pulse signal corresponding to a moving distance of the mouse device in the Y direction.
On the contrary, the optical mouse device must use a transparent board (celluloid board) exclusively. Grids having different colors are printed on the celluloid board in longitudinal and horizontal directions. In addition, the optical mouse device has an X-direction photo sensor for detecting colors of the grids only in the horizontal direction (i.e., the X direction) and a Y-direction photo sensor for detecting colors of the grids only in the longitudinal direction (i.e., the Y direction). Each photo sensor consists of a pair of a light emitting element and a light receiving element. The X-direction and Y-direction photo sensors detect numers of the grids in the horizontal and longitudinal directions to thereby detect the moving distance of the optical mouse device in the X and Y directions respectively.
However, the conventional mechanical mouse device described suffers following problems.
(1) The mechanical mouse device must have a heavy weight since the large metal ball 4 is provided therein. Hence, the mouse device will be seriously damaged when the mouse device is dropped.
(2) In the case where a frictional resistance between the metal ball 4 and a plane (e.g., a surface of desk) touching the surface of the metal ball 4 is so small that the metal ball 4 sometimes slips on the plane without revolving, the metal ball 4 does not revolve in response to the moving distance of the mouse device. Hence, it becomes sometimes impossible to input the coordinates to the personal computer system accurately.
(3) Since dust adheres to the metal ball 4 interferes with operation of the mouse device, the metal ball 4 must be cleaned up frequently.
On the other hand, the conventional optical mouse device described suffers following problems.
(a) It is burdensome for the operator to use the celluloid board exclusively used for the optical mouse device.
(b) In case where the dust adheres to the light emitting and receiving planes of the photo sensor, it sometimes becomes impossible to input the coordinates to the personal computer system accurately.